Mirror assembly for light steering

ABSTRACT

Embodiments of the disclosure provide an apparatus for adjusting a light beam that includes a microelectromechanical system (MEMS), a non-MEMS system. The MEMS may include: an array of first rotatable mirrors to receive and reflect the light beam and an array of first actuators configured to rotate each rotatable mirror of the array of first rotatable mirrors. The non-MEMS system may include a second adjustable mirror to receive and reflect the light beam and a second actuator configured to adjust the second adjustable mirror. The light beam received by the array of first rotatable mirrors is the light beam reflected by the second adjustable mirror or the light beam received by the second adjustable mirror is reflected by the array of first rotatable mirror.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 16/213,992, filed on Dec. 7, 2018, entitled “Mirror Assemblyfor Light Steering,” which is hereby incorporated by reference in itsentirety.

BACKGROUND

Light steering typically involves the projection of light in apre-determined direction to facilitate, for example, the detection andranging of an object, the illumination and scanning of an object, or thelike. Light steering can be used in many different fields ofapplications including, for example, autonomous vehicles, medicaldiagnostic devices, etc.

Light steering can be performed in both transmission and reception oflight. For example, a light steering system may include a micro-mirrorarray to control the projection direction of light to detect/image anobject. Moreover, a light steering receiver may also include amicro-mirror array to select a direction of incident light to bedetected by the receiver, to avoid detecting other unwanted signals. Themicro-mirror array may include an array of micro-mirror assemblies, witheach micro-mirror assembly comprising a micro-mirror and an actuator. Ina micro-mirror assembly, a mirror-mirror can be connected to a substratevia a connection structure (e.g., a torsion bar, a spring, etc.) to forma pivot, and the micro-mirror can be rotated around the pivot by theactuator. Each micro-mirror can be rotated by a rotation angle toreflect (and steer) light from a light source towards at a targetdirection. Each micro-mirror can be rotated by the actuator to provide afirst range of angles of projection along a vertical axis and to providea second range of angles of projection along a horizontal axis. Thefirst range and the second range of angles of projection can define atwo-dimensional field of view (FOV) in which light is to be projected todetect/scan an object. The FOV can also define the direction of incidentlights, reflected by the object, are to be detected by the receiver.

The mirror assembly can dominate various performance metrics of thelight steering system including, for example, precision, actuationpower, FOV, dispersion angle, reliability, etc. It is desirable toprovide a mirror assembly that can improve these performance metrics.

BRIEF SUMMARY

In one aspect, embodiments of the disclosure provide an apparatus foradjusting a light beam that includes a microelectromechanical system(MEMS), a non-MEMS system. The MEMS may include: an array of firstrotatable mirrors to receive and reflect the light beam and an array offirst actuators configured to rotate each rotatable mirror of the arrayof first rotatable mirrors. The non-MEMS system may include a secondadjustable mirror to receive and reflect the light beam and a secondactuator configured to adjust the second adjustable mirror. The lightbeam received by the array of first rotatable mirrors is the light beamreflected by the second adjustable mirror or the light beam received bythe second adjustable mirror is reflected by the array of firstrotatable mirror.

In another aspect, embodiments of the disclosure provide a LightDetection and Ranging system. The system may include a light source, areceiver, a microelectromechanical system (MEMS), and a non-MEMS system.The MEMS may include: an array of first rotatable mirrors to receive andreflect the light beam and an array of first actuators configured torotate each rotatable mirror of the array of first rotatable mirrors.The non-MEMS system may include a second adjustable mirror to receiveand reflect the light beam and a second actuator configured to adjustthe second adjustable mirror. The light beam received by the array offirst rotatable mirrors is the light beam reflected by the secondadjustable mirror or the light beam received by the second adjustablemirror is reflected by the array of first rotatable mirror.

In a further aspect, embodiments of the disclosure further provide amethod for adjusting a light beam in a light steering system. The methodmay include determining a first angle and a second angle of a lightpath, the light path being a projection path for an output light or aninput path of an input light, the first angle being with respect to afirst dimension, the second angle being with respect to a seconddimension orthogonal to the first dimension and controlling an array offirst actuators to rotate an array of first rotatable micro-mirrors of amicroelectromechanical system (MEMS) to set the first angle. The methodmay also include controlling a second non-MEMS system to set the secondangle and projecting, using a light source, a light beam including alight signal towards a mirror assembly, corresponding to the controlledarray of first actuators and the controlled non-MEMS system at the setfirst and second angle. The method may further include performing atleast one of: reflecting the output light from the light source alongthe projection path towards an object or reflecting the input lightpropagating along the input path to a receiver.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures.

FIG. 1 shows an autonomous driving vehicle utilizing aspects of certainembodiments of the disclosed techniques herein.

FIG. 2 illustrates an example of a light steering system, according tocertain embodiments.

FIG. 3A-FIG. 3E illustrate an example of a mirror assembly and itsoperations, according to certain embodiments.

FIG. 4 illustrates an example of operation of the mirror assembly ofFIG. 3A-FIG. 3E to provide a two-dimensional field of view (FOV),according to certain embodiments.

FIG. 5A and FIG. 5B illustrate another example of a mirror assembly,according to certain embodiments.

FIG. 6 illustrates another example of a mirror assembly, according tocertain embodiments.

FIG. 7 illustrates another example of a mirror assembly, according tocertain embodiments.

FIG. 8 illustrates another example of a mirror assembly, according tocertain embodiments.

FIG. 9 illustrates a flowchart of a method of operating a mirrorassembly, according to embodiments of the disclosure.

FIG. 10 illustrates an example computer system that may be utilized toimplement techniques disclosed herein.

DETAILED DESCRIPTION

Aspects of the present disclosure relate generally to peripheraldevices, and in particular to a wireless peripheral device controller,according to certain examples.

In the following description, various examples of a mirror assembly anda light steering system will be described. For purposes of explanation,specific configurations and details are set forth in order to provide athorough understanding of the embodiments. However, it will be apparentto one skilled in the art that certain embodiments may be practiced orimplemented without every detail disclosed. Furthermore, well-knownfeatures may be omitted or simplified in order to prevent anyobfuscation of the novel features described herein.

Light steering can be found in different applications. For example, aLight Detection and Ranging (LiDAR) module of a vehicle may include alight steering system. The light steering system can be part of thetransmitter to steer light towards different directions to detectobstacles around the vehicle and to determine the distances between theobstacles and the vehicle, which can be used for autonomous driving.Moreover, a light steering receiver may also include a micro-mirrorarray to select a direction of incident light to be detected by thereceiver, to avoid detecting other unwanted signals. Further, the headlight of a manually-driven vehicle can include the light steeringsystem, which can be controlled to focus light towards a particulardirection to improve visibility for the driver. In another example,optical diagnostic equipment, such as an endoscope, can include a lightsteering system to steer light in different directions onto an object ina sequential scanning process to obtain an image of the object fordiagnosis.

Light steering can be implemented by way of a micro-mirror array. Themicro-mirror array can have an array of micro-mirror assemblies, witheach micro-mirror assembly having a movable micro-mirror and an actuator(or multiple actuators). The micro-mirrors and actuators can be formedas microelectromechanical systems (MEMS) on a semiconductor substratewhich allows integration of the MEMS with other circuitries (e.g.,controller, interface circuits, etc.) on the semiconductor substrate. Ina micro-mirror assembly, a mirror-mirror can be connected to thesemiconductor substrate via a connection structure (e.g., a torsion bar,a spring, etc.) to form a pivot. The actuator can rotate themicro-mirror around the pivot, with the connection structure deformed toaccommodate the rotation. The array of micro-mirrors can receiveincident light beam, and each micro-mirror can be rotated at a commonrotation angle to project/steer the incident light beam at a targetdirection. Each micro-mirror can be rotated around two orthogonal axesto provide a first range of angles of projection along a verticaldimension and to provide a second range of angles of projection along ahorizontal dimension. The first range and the second range of angles ofprojection can define a two-dimensional field of view (FOV) in whichlight is to be projected to detect/scan an object. The FOV can alsodefine the direction of incident lights, reflected by the object, are tobe detected by the receiver.

In some examples, each micro-mirror assembly may include a singlemicro-mirror. The single micro-mirror can be coupled with a pair ofactuators on a frame of a gimbal structure and rotatable on a firstaxis. The frame of the gimbal structure is further coupled with thesemiconductor substrate and rotatable on a second axis orthogonal to thefirst axis. A first pair of actuators can rotate the mirror around thefirst axis with respect to the frame to steer the light along a firstdimension, whereas a second pair of actuators can rotate the framearound a second axis to steer the light along a second dimension.Different combinations of angle of rotations around the first axis andthe second axis can provide a two-dimensional FOV in which light is tobe projected to detect/scan an object. The FOV can also define thedirection of incident lights, reflected by the object, are to bedetected by the receiver.

Although such arrangements allow the projection of light to form atwo-dimensional FOV, there may be a number of potential disadvantages.First, having a single mirror to provide light steering can require arelatively high actuation force to achieve a target FOV and a targetdispersion, which can reduce reliability. More specifically, to reducedispersion, the size of the mirror can be made to match the width of thelight beam from the light source, which leads to increased mass andinertia of the mirror. As a result, a larger actuation force (e.g.,torque) may be needed to rotate the mirror to achieve a target FOV. Thetorque required typically is in the order of micro N-m. Subjecting theactuators to larger actuation forces, especially for MEMS actuators, canshorten the lifespan and reduce the reliability of the actuators.Moreover, the reliability of the MEMS actuators may be further degradedwhen the light steering system relies solely on the single mirror tosteer the light, which can become a single point of failure.

Conceptual Overview of Certain Embodiments

Examples of the present disclosure relate to a light steering systemthat can address the problems described above. Various embodiments ofthe light steering system can include a plurality of mirrors to performlight steering, such as those shown and described below with respect toFIG. 3A-FIG. 3E, FIG. 5A, FIG. 6, FIG. 7 and FIG. 8. The light steeringsystem can be used as part of a transmitter to control a direction ofprojection of output light. The light steering system can also be usedas part of a receiver to select a direction of input light to bedetected by the receiver. The light steering system can also be used ina coaxial configuration such that the light steering system can projectoutput light to a location and detects light reflected from thatlocation.

In some embodiments, a light steering system may include a light source,a first rotatable mirror, a second rotatable mirror, and a receiver. Thefirst rotatable mirror and the second rotatable mirror can define anoutput projection path for light transmitted by the light source, or toselect an input path for input light to be received by the receiver. Thefirst rotatable mirror and the second rotatable mirror can be rotatableto steer the output projection path at different angles with respect to,respectively, a first dimension and a second dimension orthogonal to thefirst dimension, to form a two-dimensional FOV.

The light steering system may further include a first actuatorconfigured to rotate the first rotatable mirror around a first axis, asecond actuator configured to rotate the second rotatable mirror arounda second axis orthogonal to the first axis, and a controller coupledwith the first actuator and the second actuator. The controller maycontrol the first actuator and the second actuator to apply a firsttorque and a second torque to rotate, respectively, the first rotatablemirror and the second rotatable mirror along, respectively, the firstaxis and the second axis. The controller can control the first actuatorand the second actuator to steer the output projection path at differentangles with respect to the first dimension and the second dimensionaccording to a movement sequence, such as those shown and describedbelow with respect to FIG. 4 and FIG. 5B, to create the two-dimensionalFOV.

In some embodiments, the first rotatable mirror and the second rotatablemirror can be arranged on the same surface of a semiconductor substrate,as shown in FIG. 3A. The light steering system can further include astationary third mirror stacked on top of the semiconductor substrateand facing the surface of the semiconductor substrate. As shown in FIG.3B, light from the light source, or input light from the environment,can be reflected by the first rotatable mirror, which can set a firstangle of the output projection path of the light with respect to thefirst dimension (e.g., an x-axis or a y-axis). The light reflected bythe first rotatable mirror can reach the third mirror, which may reflectthe light towards the second rotatable mirror. The second rotatablemirror can set an angle of the output projection path or an input pathwith respect to the second dimension (e.g., the z-axis of FIG. 4D).Different values of the first angle and the second angle can be obtainedby rotating the first rotatable mirror and the second rotatable mirrorto form the FOV.

In some embodiments, as shown in FIG. 3A, the light steering system caninclude a first array of mirrors including the first rotatable mirror,with each rotatable mirror of the array rotatable around the first axis,and a single second rotatable mirror rotatable around the second axis.In some embodiments, as shown in FIG. 5A, the light steering system canalso include a single first rotatable mirror, and an array of secondrotatable mirrors, with each rotatable mirror of the array rotatablearound the second axis. In some embodiments, as shown in FIG. 6, thelight steering system can also include a first array of rotatablemirrors and a second array of rotatable mirrors. The first array ofrotatable mirrors may be rotatable around the first axis. Moreover, thesecond array of mirrors may be rotatable around the second axis.

In some embodiments, the first rotatable mirror and the second rotatablemirror can be arranged on two different semiconductor substrates, asshown and described below with respect to FIG. 7. The first rotatablemirror can be arranged on a first surface of the first semiconductor,whereas the second rotatable mirror can be arranged on a second surfaceof the second semiconductor, with the first surface facing the secondsurface. Light from the light source can be reflected by the firstrotatable mirror, which can set the first angle of the output projectionpath or input path with respect to the first dimension (e.g., the x-axisor the y-axis). The light reflected by the first rotatable mirror canreach the second rotatable mirror, which can rotate around the secondaxis to set a second angle of the output projection path or the inputpath with respect to the second dimension (e.g., the z-axis).

Compared with an arrangement where a light steering system uses a singlemirror having two axis of rotation to provide two ranges of projectionor input angles to form a FOV, certain embodiments of the presentdisclosure can use a first rotatable mirror and a second rotatablemirror (or an array of first rotatable mirrors and a second rotatablemirror) with each having a single but orthogonal rotational axis toprovide the two ranges of angles that form the FOV. Such arrangementscan improve reliability (especially where the mirrors are MEMS devices)and precision, and can reduce actuation power, while providing the sameor superior FOV and dispersion. First, by using two mirrors to providetwo ranges of angles to provide the same FOV as the single mirror, someof the mirrors can be made smaller than the single mirror and mayrequire less actuation force to rotate than the single mirror. Theactuation of the two different mirrors can also be independentlyoptimized to further reduce the total actuation force. The reduction ofthe actuation forces can also reduce the burden on the actuators andincreases the lifespan of the actuators. Moreover, due to the smallermirrors, embodiments of the present disclosure can provide a larger FOVcompared with the single mirror implementation in response to the sameactuation force. The mirrors can be configured to provide the samemirror surface area as the single mirror, which can provide the samedispersion as the single mirror. In addition, where a plurality ofmirrors is involved in the steering of light, the likelihood that any ofthe mirrors becoming a single source of failure can be mitigated, whichcan further improve reliability. All of these can improve the robustnessand performance of a light steering system over conventionalimplementations.

Typical System Environment for Certain Embodiments

FIG. 1 illustrates an autonomous vehicle 100 in which the disclosedtechniques can be implemented. Autonomous vehicle 100 includes a LiDARmodule 102. LiDAR module 102 allows autonomous vehicle 100 to performobject detection and ranging in a surrounding environment. Based on theresult of object detection and ranging, autonomous vehicle 100 canmaneuver to avoid a collision with the object. LiDAR module 102 caninclude a light steering system 104 and a receiver 106. Light steeringsystem 104 can project one or more light signals 108 at variousdirections at different times in any suitable scanning pattern, whilereceiver 106 can monitor for a light signal 110 which is generated bythe reflection of light signal 108 by an object. Light signals 108 and110 may include, for example, a light pulse, a frequency modulatedcontinuous wave (FMCW) signal, an amplitude modulated continuous wave(AMCW) signal, etc. LiDAR module 102 can detect the object based on thereception of light signal 110, and can perform a ranging determination(e.g., a distance of the object) based on a time difference betweenlight signals 108 and 110. For example, as shown in FIG. 1, LiDAR module102 can transmit light signal 108 at a direction directly in front ofautonomous vehicle 100 at time T1 and receive light signal 110 reflectedby an object 112 (e.g., another vehicle) at time T2. Based on thereception of light signal 110, LiDAR module 102 can determine thatobject 112 is directly in front of autonomous vehicle 100. Moreover,based on the time difference between T1 and T2, LiDAR module 102 canalso determine a distance 114 between autonomous vehicle 100 and object112. Autonomous vehicle 100 can adjust its speed (e.g., slowing orstopping) to avoid collision with object 112 based on the detection andranging of object 112 by LiDAR module 102.

FIG. 2A-2B illustrate examples of internal components of a LiDAR module102. LiDAR module 102 includes a transmitter 202, a receiver 204, aLiDAR controller 206 which controls the operations of transmitter 202and receiver 204. Transmitter 202 includes a light source 208 and acollimator lens 210, whereas receiver 204 includes a lens 214 and aphotodetector 216. LiDAR module 102 further includes a mirror assembly212 and a beam splitter 213. In LiDAR module 102, transmitter 202 andreceiver 204 can be configured as a coaxial system to share mirrorassembly 212 to perform light steering operation, with beam splitter 213configured to reflect incident light reflected by mirror assembly 212 toreceiver 204.

FIG. 2A illustrates a light projection operation. To project light,LiDAR controller 206 can control light source 208 (e.g., a pulsed laserdiode, a source of FMCW signal, AMCW signal, etc.) to transmit lightsignal 108 as part of light beam 218. Light beam 218 can disperse uponleaving light source 208 and can be converted into collimated light beam218 by collimator lens 210.

Collimated light beam 218 can be incident upon mirror assembly 212,which can reflect and steer the light beam along an output projectionpath 219 towards object 112. Mirror assembly 212 can include one or morerotatable mirrors. FIG. 2A illustrates mirror assembly 212 as having onemirror, but as to be described below, in some embodiments mirrorassembly 212 may include a plurality of mirrors.

Light beam 218 may disperse upon leaving the surface of mirror surfaceof mirror assembly 212. Light beam 218 can form a dispersion angle withrespect to projection path 219 over the length and the width of themirror surface. The dispersion angle of light beam 218 can be given bythe following equation:

$\begin{matrix}{\alpha = \frac{\lambda}{D \times \pi}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

In Equation 1, α is the dispersion angle, λ is the wavelength of lightbeam 218, whereas D is the length (or width) of the mirror surface.Light beam 218 can disperse at a dispersion angle α_(L) with respect toprojection path 219 over the length (L) of the mirror surface, and at adispersion angle α_(w) with respect to projection path 219 over thewidth (W) of the mirror surface. It is desirable to reduce thedispersion angle to focus the light beam power along projection path219, to improve the resolution of object detection, ranging, andimaging. To reduce the dispersion angle, the length and width D of themirror surface can be increased to match with aperture length 220.

Mirror assembly 212 further includes one or more actuators (not shown inFIG. 2A) to rotate the rotatable mirrors. The actuators can rotate therotatable mirrors around a first axis 222 and can rotate the rotatablemirrors along a second axis 226. As described in more detail below, therotation around first axis 222 can change a first angle 224 of outputprojection path 219 with respect to a first dimension (e.g., thex-axis), whereas the rotation around second axis 226 can change a secondangle 228 of output projection path 219 with respect to a seconddimension (e.g., the z-axis). LiDAR controller 206 can control theactuators to produce different combinations of angles of rotation aroundfirst axis 222 and second axis 226 such that the movement of outputprojection path 219 can follow a scanning pattern 232. A range 234 ofmovement of output projection path 219 along the x-axis, as well as arange 238 of movement of output projection path 219 along the z-axis,can define a FOV. An object within the FOV, such as object 112, canreceive and reflect collimated light beam 218 to form reflected lightsignal, which can be received by receiver 204.

FIG. 2B illustrates a light detection operation. LiDAR controller 206can select an incident light direction 239 for detection of incidentlight by receiver 204. The selection can be based on setting the anglesof rotation of the rotatable mirrors of mirror assembly 212, such thatonly light beam 220 propagating along light direction 239 gets reflectedto beam splitter 213, which can then divert light beam 220 tophotodetector 216 via collimator lens 214. With such arrangements,receiver 204 can selectively receive signals that are relevant for theranging/imaging of object 112, such as light signal 110 generated by thereflection of collimated light beam 218 by object 112, and not toreceive other signals. As a result, the effect of environmentdisturbance on the ranging/imaging of the object can be reduced, and thesystem performance can be improved.

Examples of Mirror Assemblies

FIG. 3A-FIG. 3E illustrate an example of a mirror assembly 300,according to embodiments of the present disclosure. Mirror assembly 300can be part of light steering system 202. FIG. 3A illustrates a top viewof mirror assembly 300, FIG. 3B illustrates a perspective view of mirrorassembly 300, whereas FIG. 3C illustrates a side view of mirror assembly300. As shown in FIG. 3A, mirror assembly 300 can include an array offirst rotatable mirrors 302, a second rotatable mirror 304, and astationary mirror 306. The total mirror surface area of the array offirst rotatable mirrors 302 is identical to the mirror surface area ofsecond rotatable mirror 304 and of stationary mirror 306. The array offirst rotatable mirrors 302 and second rotatable mirror 304 can be MEMSdevices implemented on a surface 308 of a semiconductor substrate 310.Stationary mirror 306 can be positioned above semiconductor substrate310. In some embodiments, stationary mirror 306 can be included withinthe same integrated circuit package as semiconductor substrate 310 toform an integrated circuit. In some embodiments, stationary mirror 306can also be positioned external to the integrated circuit package thathouses semiconductor substrate 310.

Referring to FIG. 3B and FIG. 3C, in one configuration, array of firstrotatable mirrors 302 can receive collimated light beam 218 fromcollimator lens 210, reflect the light beam 218 towards stationarymirror 306, which can reflect the light beam 218 towards secondrotatable mirror 304. Second rotatable mirror 304 can reflect light beam218 received from stationary mirror 306 as an output along outputprojection path 219. In another configuration (not shown in thefigures), second rotatable mirror 304 can receive collimated light beam218 from collimator lens 210 and reflect the light beam 218 towardsstationary mirror 306, which can reflect the light beam 218 towardsarray of first rotatable mirrors 302. Array of first rotatable mirrors302 can reflect light beam 218 as an output along output projection path219. In a case where mirror assembly 300 is part of the receiver, thearray of first rotatable mirrors 302 and second rotatable mirror 304 canalso select incident light direction 239 for receiver 204 similar to theselection of direction of output projection path 219. As described infurther detail below, array of first rotatable mirrors 302 and secondrotatable mirror 304 change an angle of output projection path 219 withrespect to, respectively, the x-axis and the z-axis, to form atwo-dimensional FOV.

As described above, the total mirror surface area of the array of firstrotatable mirrors 302 is identical to the mirror surface area of secondrotatable mirror 304 and of stationary mirror 306. Moreover, eachdimension (e.g., length and width) of the mirror surface area providedby each of the array of first rotatable mirrors 302, second rotatablemirror 304, and stationary mirror 306 can match aperture length 220 ofcollimator lens 210. With such arrangements, each of the array of firstrotatable mirrors 302, second rotatable mirror 304, and stationarymirror 306 can receive and reflect a majority portion of collimatedlight beam 218.

Moreover, as shown in FIG. 3C, the separation between stationary mirror306 and surface 308 (which includes an array of first rotatable mirrors302 and second rotatable mirror 304, denoted as d1, as well as theseparation between the center points of an array of first rotatablemirrors 302 and second rotatable mirror 304, denoted as d2, can berelated to incident angle θ of collimated light beam 218 with respect tothe z-axis, as follows:

$\begin{matrix}{\frac{\frac{d\; 2}{2}}{d\; 1} = {\tan(\theta)}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

In Equation 2, the ratio between half of d2 (the distance between thecenter points of an array of first rotatable mirrors 302 and secondrotatable mirror 304) and d1 (the distance between stationary mirror 306and surface 308) can be defined by applying tangent function to theincident angle θ of collimated light beam 218.

Referring back to FIG. 3A, each rotatable mirror of the array of firstrotatable mirrors 302 (e.g., first rotatable mirror 302 a) is rotatablearound a first axis 314, whereas second rotatable mirror 304 isrotatable around a second axis 316 which is orthogonal to first axis314. Each rotatable mirror of the array of first rotatable mirrors 302,as well as second rotatable mirror 304, is coupled with a pair of rotaryactuators, such as comb drive, piezoelectric device, electromagneticdevice, etc., to rotate the mirror. For example, first rotatable mirror302 a is coupled with and rotary actuators 322 a and 322 b, whereassecond rotatable mirror 304 is coupled with rotary actuators 324 a and324 b. Each of first rotatable mirror 302 a (and the rest of array offirst rotatable mirrors 302) and second rotatable mirror 304 canindependently move output projection path 219 along, respectively, thex-axis and the z-axis, to form a FOV.

FIG. 3D illustrates an example of setting an angle of output projectionpath 219 with respect to the x-axis based on the rotation movement offirst rotatable mirror 302 a. FIG. 3D shows a side view of rotatablemirror 302 a with first axis 314, stationary mirror 306, and secondrotatable mirror 304. First axis 314 is aligned with the y-axis. Thedotted lines show the orientations of first rotatable mirror 302 a andnormal vector 330 of first rotatable mirror 302 a before rotation, whilethe solid lines show the orientations of first rotatable mirror 302 aand normal vector 330 after a counter-clockwise rotation. As firstrotatable mirror 302 a rotates counter-clockwise, normal vector 330 offirst rotatable mirror 302 a also rotates counter-clockwise, and theangle of incidence 332 of collimated light beam 218 with respect to therotated normal vector 330 reduces. As the angle of reflection 334 ofcollimated light beam 218 is equal to the angle of incidence 332, thereflected light beam 218 also rotates counter-clockwise and hitstationary mirror 306 at an increased angle 336. Light beam 218 is alsoreflected from stationary mirror 306 at the same angle 336 towardssecond rotatable mirror 304, which can reflect light beam 218 alongoutput projection path 219 or input path 239 that also forms angle 336with the x-axis. Each rotatable mirror of the array of first rotatablemirrors 302 can be controlled to rotate by the same angle of rotationand at the same direction (clockwise or counterclockwise) around firstaxis 314, so that the array can collectively set output projection path219 of collimated light beam 218, or incident light direction 239, toform angle 336 with respect to the x-axis.

FIG. 3E illustrates an example of movement of output projection path 219based on the rotation movement of second rotatable mirror 304. FIG. 3Eis a side view of second rotatable mirror 304 with second axis 316pointing out of paper. The dotted lines show the orientations of secondrotatable mirror 304 and normal vector 340 of second rotatable mirror304 before rotation, while the solid lines show the orientations ofsecond rotatable mirror 304 and normal vector 340 after acounter-clockwise rotation. As second rotatable mirror 304 rotatescounter-clockwise, normal vector 340 of second rotatable mirror 304 alsorotates counter-clockwise, and the angle of incidence 342 of collimatedlight beam 218 with respect to the rotated normal vector 340 reduces. Asthe angle of reflection 344 of collimated light beam 218 is equal to theangle of incidence 342, output projection path 219 of reflected lightbeam 218 moves along the z-axis by a distance d4 as indicated by thearrow. Combined with the rotation of first rotatable mirror 302 a,output projection path 219 can move along both the x-axis and the z-axisto form a two-dimensional FOV. It is understood that incident lightdirection 239 can also be adjusted based on the rotation movement ofsecond rotatable mirror 304 in a similar fashion as output projectionpath 219.

FIG. 4 illustrates an example operation of mirror assembly 300 toprovide a two-dimensional FOV. The diagram on the top of FIG. 4illustrates a movement sequence 400 of an angle of output projectionpath 219 provided by the rotations of array of first rotatable mirrors302 and second rotatable mirror 304. As shown in FIG. 4, LiDARcontroller 206 can control rotary actuators 324 a and 324 b to rotatesecond rotatable mirror 304 to set different angles of output projectionpath 219 with respect to the z-axis, for example, at angles representedby points 402 and 404, to within a first angle range 406. LiDARcontroller 206 can also control the rotary actuators of array of firstrotatable mirrors 302 (e.g., rotary actuators 322 a and 322 b) to setdifferent angles of output projection path 219 with respect to thex-axis, for example, at angles represented by points 412 and 414, toprovide a second angle range 416, and the two angle ranges can define aFOV.

The figure on the bottom of FIG. 4 illustrates a control signalssequence 430, with respect to time, to generate movement sequence 400 ofoutput projection path 219. In some embodiments, movement sequence 400can be provided to LiDAR controller 206, which can generate controlsignals sequence 430 based on movement sequence 400. Control signalssequence 430 comprises first dimension control signals sequences 432,434, 436, etc., of control signals for the rotary actuators of secondrotatable mirrors 304 to change the angle of output projection path 219(or incident light direction 239) with respect to a first dimension(e.g., z-axis). Control signals sequence 430 further include a seconddimension control signal between two first dimension control signalssequences. For example, there is a second dimension control signal 440between first dimension control signals sequences 432 and 434. Further,there is a second dimension control signal 442 between first dimensioncontrol signals sequences 434 and 436. The second dimension controlsignals are for the rotary actuators of array of first rotatable mirrors302 to change the angle of output projection path 219 (or incident lightdirection 239) with respect to a second dimension (e.g., x-axis).

Each control signal in control signals sequences 432, 434, 436, etc.,can cause the rotary actuators of second rotatable mirror 304 togenerate a torque force to increment the angle of rotation of the secondrotatable mirror 304 around second axis 316. For example, firstdimension control signal 432 a can correspond to point 402, whereasfirst dimension control signal 432 b can correspond to point 404. Eachof first dimension control signals sequences 432, 434, and 436 can causea sweep of angles of output projection path 219 (or incident lightdirection 239) across first angle range 406 with respect to the z-axisby controlling the angle of rotation of the second rotatable mirror. Atthe end of first angle range 406, a second dimension control signal canbe provided to change the angle of projection path 219 (or incidentlight direction 239) with respect to the x-axis before the next firstdimension control signals sequence starts. For example, first dimensioncontrol signal 432 n corresponds to point 412 which is at the end offirst angle range 406. Following first dimension control signal 432 b issecond dimension control signal 440, which can rotate array of firstrotatable mirrors 302 to move output projection path 219 (or incidentlight direction 239) from points 412 to 414 along the x-axis. Followingsecond dimensional control signal 440, first dimension control signalssequence 434 starts, and first dimension control signal 434 a can rotatesecond rotatable mirror 304 to move the angle of output projection path219 (or incident light direction 239) with respect to the z-axis from anangle represented by point 414 to an angle represented by 418, whilekeeping the angle with respect to the x-axis constant.

In some embodiments, first dimension control signals and seconddimension control signals can be independently optimized to reduce totalactuation forces and power. For example, first dimension control signalscan be provided to the rotary actuators at a relatively high frequencyclose to the natural frequency of second rotatable mirror 304 to induceharmonic resonance of the mirror. Such arrangements allow use of smallertorques to rotate second rotatable mirror 304, which is advantageousgiven that second rotatable mirror 304 can be the largest mirror withinmirror assembly 300 and has considerable mass and inertia. On the otherhand, second dimension control signals can be provided to the rotaryactuators at a relatively low frequency to operate each rotatable mirrorof array of first rotatable mirrors 302 as quasi-static loads. Thetorques required to rotate the mirrors of array of first rotatablemirrors 302 may be relatively low, given that the mirrors are small andhave small mass and inertia. In some embodiments, first dimensioncontrol signals can be in the form of high frequency sinusoidal signals,pulse width modulation (PWM) signals, etc., whereas second dimensioncontrol signals can be in the form of low frequency saw-tooth signals.

In some embodiments, in addition to movement sequence 400, a feedbackmechanism can also be provided to LiDAR controller 206 to generatecontrol signals sequence 430. The feedback mechanism includes a set ofsensors (e.g., capacitive sensors) to measure actual angles of rotationat the rotary actuators. The feedback mechanism enables LiDAR controller206 to adjust the first dimension and second dimension control signalsprovided to the rotary actuators based on monitoring the actual angle ofrotations at the rotary actuators, to improve the precision of the lightsteering operation. The adjustment can be performed to compensate for,for example, uncertainties and mismatches in the masses of the mirrors,driving strength of the rotary actuators, etc.

As an example, LiDAR controller 206 can perform adjustment of the firstdimension and second dimension control signals in a calibrationsequence. LiDAR controller 206 may store a set of initial settings(e.g., voltage, current, etc.) for the first dimension and seconddimension control signals based on a set of expected masses of themirrors and driving strength of the rotary actuators. During thecalibration process, LiDAR controller 206 can provide different firstdimension and second dimension control signals to create differentangles of rotations at the rotary actuators. LiDAR controller 206 canmonitor the actual angles of rotations at the rotary actuators when thefirst dimension and second dimension control signals are provided,compare the actual angles of rotations against the target angles ofrotations to determine differences, and adjust the first dimension andsecond dimension control signals to account for the differences. Forexample, each rotatable mirror of array of first rotatable mirrors 302is supposed to rotate at the same angle of rotation. LiDAR controller206 can measure the actual angles of rotation of each rotatable mirrorof array of first rotatable mirrors 302 using the capacitive sensors anddetermine a deviation of each actual angle from the target angle ofrotation for each rotatable mirror. LiDAR controller 206 can adjust thesecond dimension control signals for the rotary actuators of eachrotatable mirror (e.g., rotary actuators 322 a and 322 b) based on thedeviations to ensure that each rotatable mirror rotates by the sametarget angle of rotation.

Compared with a single mirror assembly, mirror assembly 300 can providesame or superior FOV and dispersion performance while reducing theactuation force and power and improving reliability. First, eachrotatable mirror of the array of first rotatable mirrors 302 issubstantially smaller than a single mirror having a comparable lengthand width and dispersion performance, even if the mirrors are driven asquasi-static loads. As a result, each rotatable mirror of the array offirst rotatable mirrors 302 requires substantially smaller torque toprovide the same FOV as the single mirror assembly. Moreover, althoughthe mirror surface area of the second rotatable mirror 304 is similar tothe area of the single mirror arrangement, the torque needed to rotatesecond rotatable mirror 304 can be substantially reduced by drivingsecond rotatable mirror 304 at close to a natural frequency to induceharmonic resonance. Such arrangements allows substantial reduction inthe required torque to achieve a target FOV. The reduction of torquealso reduces the burden on the rotary actuators and increases theirlifespan. In addition, as a plurality of mirrors are involved in thesteering of light, the likelihood of any of the mirror becoming a singlesource of failure can be mitigated, which can further improvereliability.

FIG. 5A illustrates another example of a mirror assembly 500, accordingto embodiments of the present disclosure. Mirror assembly 500 can bepart of light steering system 202. As shown in FIG. 5A, mirror assembly500 can include a first rotatable mirror 502, an array of secondrotatable mirrors 504, and stationary mirror 306. Each of firstrotatable mirror 502, array of second rotatable mirror 504, andstationary mirror 306 can have substantially same mirror surface areaand can have dimensions matching aperture length 220 of lens 210, as inother examples described above. First rotatable mirror 502, an array ofsecond rotatable mirrors 504 can be MEMS devices implemented on asurface 508 of a semiconductor substrate 510. Stationary mirror 306 canbe positioned above semiconductor substrate 510. First rotatable mirror502 may receive collimated light beam 218 from lens 210, reflect thecollimated light beam 218 towards stationary mirror 306, which can inturn reflect collimated light beam 218 towards array of second rotatablemirrors 504. Array of second rotatable mirrors 504 can reflect thecollimated light beam 218 received from stationary mirror 306 as outputalong output projection path 219. First rotatable mirror 502 isrotatable around a first axis 514, whereas each rotatable mirror of thearray of second rotatable mirrors 504 is rotatable around a second axis516 which is orthogonal to first axis 514. Just as array of firstrotatable mirrors 302 of FIG. 3A, the rotation of first rotatable mirror502 can set an angle of output projection path 219 (or incident lightdirection 239) with respect to the x-axis, whereas the rotation of arrayof second rotatable mirrors 504 can set an angle of output projectionpath 219 (or incident light direction 239) with respect to the z-axis.

First rotatable mirror 502 and array of second rotatable mirror 504 canindependently change the angle of output projection path 219 (orincident light direction 239) with respect to, respectively, the x-axisand the z-axis, to form a two-dimensional FOV. The rotation of firstrotatable mirror 502 and array of second rotatable mirrors 504 can becontrolled based on a movement sequence 550 of FIG. 5B. First rotatablemirror 502 can be controlled by first dimension control signals to moveoutput projection path 219 (or incident light direction 239) along thex-axis within a movement range 552, whereas array of second rotatablemirrors 504 can be controlled by second dimension control signals tomove projection path along the z-axis within a movement range 554.Similar to the arrangements described in FIG. 4, first dimension controlsignals can be provided at a relatively high frequency close to thenatural frequency of first rotatable mirror 502 to induce harmonicresonance, whereas second dimension control signals can be provided at arelatively low frequency to drive each of the array of second rotatablemirrors 504 as quasi-static loads.

In some examples, a mirror assembly can include two arrays of rotatablemirrors to perform light steering along a first dimension (e.g., thex-axis) and a second dimension (e.g., the z-axis). FIG. 6 illustrates anexample of a mirror assembly 600 that includes array of first rotatablemirrors 302 of FIG. 3A and array of second rotatable mirrors 504 of FIG.5A on a surface 608 of a semiconductor substrate 610. Mirror assembly600 further includes stationary mirror 306 positioned abovesemiconductor substrate 610. Array of first rotatable mirrors 302 isrotatable around first axis 314, whereas array of second rotatablemirrors 504 is rotatable around second axis 516 which is orthogonal tofirst axis 314. Array of first rotatable mirrors 302 and array of secondrotatable mirror 504 can independently change the angle of outputprojection path 219 with respect to, respectively, the x-axis and thez-axis, to form a two-dimensional FOV as described above.

FIG. 7 illustrates another example of a mirror assembly 700, accordingto embodiments of the present disclosure. Mirror assembly 700 can bepart of light steering system 202. The top figure of FIG. 7 shows a topview of mirror assembly 700, whereas the bottom figure of FIG. 7 shows aperspective view of mirror assembly 700. As shown in FIG. 7, mirrorassembly 700 can include array of first rotatable mirrors 302, a secondrotatable mirror 704, and an optional mirror 706 which can be stationaryor rotatable. Array of first rotatable mirrors 302 and mirror 706 can beimplemented as a surface 708 of a first semiconductor substrate 710,whereas second rotatable mirror 704 can be implemented on a secondsemiconductor substrate (not shown in FIG. 7) and facing array of firstrotatable mirrors 302 and mirror 706. Each of array of first rotatablemirrors 302, second rotatable mirror 704, and mirror 706 may havesubstantially identical mirror surface area having each dimensionmatching aperture length 210 of lens 210, as in other examples describedabove. Array of first rotatable mirrors 302 can receive collimated lightbeam 218 (or reflected light beam 220) and reflect the light towardssecond rotatable mirror 704, which can reflect the light from array offirst rotatable mirrors 302 towards mirror 706. Mirror 706 can reflectthe light received from second rotatable mirror 704 as output alongoutput projection path 219. Mirror 706 can also reflect input lighttowards second rotatable mirror 704, and only light that propagatesalong incident light direction 239 will be reflected to array of firstrotatable mirrors 302. Array of first rotatable mirrors 302 is rotatablearound first axis 314, whereas second rotatable mirror 704 is rotatablearound second axis 724 which is orthogonal to first axis 314. Therotation of each rotatable mirror of array of first rotatable mirrors302 can set an angle of output projection path 219 (or incident lightdirection 239) with respect to the x-axis, whereas the rotation ofsecond rotatable mirror 704 can set an angle of output projection path219 (or incident light direction 239) with respect to the z-axis. Mirror706 can be stationary or can be rotatable to allow further adjustment ofthe direction of output projection path 219 (or incident light direction239).

In some embodiments, mirror assembly 212 can have a fast axis (e.g., thex-axis) driven with a sinusoidal scanning trajectory and shifting thesample in steps or continuously in a slow axis (e.g., the z-axis) with asawtooth scanning trajectory or a triangle scanning trajectory. In someembodiments, the fast axis movement can be steered by MEMS devisessimilar to embodiments disclosed in FIG. 3A, FIG. 5A, FIG. 6 and FIG. 7,and the other axis (the slow axis) movements can be steered by non-MEMSdevices such as an analog system (e.g., a system that includes at leastone of a galvanometer mirror, a mirror polygon, or flash lens). As theslow axis scanning has a lower requirement for scanning frequency,accuracy and mechanical life, using suitable non-MEMS devices to drivethe slow axis scanning can meet the requirement while significantlyreducing the complexity and the cost of establishing the mirrorassembly. FIG. 8 illustrates another example of a mirror assembly 800,according to embodiments of the present disclosure. Mirror assembly 800can be part of light steering system 202. As shown in FIG. 8, mirrorassembly 800 can include an array of first rotatable mirrors 802, asecond rotatable mirror 804 and stationary mirror 306. Each of array offirst rotatable mirrors 802, second rotatable mirror 804 and stationarymirror 306 can have substantially same mirror surface area and can havedimensions matching aperture length 220 of lens 210, as in otherexamples described above. Array of first rotatable mirrors 802 can beMEMS devices implemented on a surface 808 of a semiconductor substrate810. Second rotatable mirror 804 can be a non-MEMS device such as ananalog system (e.g., a galvanometer mirror, a mirror polygon, or flashlens devices) implemented on surface 808 of semiconductor substrate 810.Stationary mirror 306 can be positioned above semiconductor substrate810. Array of first rotatable mirrors 802 may receive collimated lightbeam 218 from lens 210, reflect the collimated light beam 218 towardsstationary mirror 306, which can in turn reflect collimated light beam218 towards second rotatable mirror 804. Second rotatable mirror 804 canreflect the collimated light beam 218 received from stationary mirror306 as output along output projection path 219. Each rotatable mirror ofarray of first rotatable mirrors 802 is rotatable around a first axis814, whereas second rotatable mirror 804 is rotatable around a secondaxis 816 which is different from first axis 814, such as orthogonal tofirst axis 814. Just as array of first rotatable mirrors 302 of FIG. 3A,the rotation of array of first rotatable mirrors 802 can set an angle ofoutput projection path 219 (or incident light direction 239) withrespect to the x-axis, whereas the rotation of second rotatable mirror804 can set an angle of output projection path 219 (or incident lightdirection 239) with respect to the z-axis.

Array of first rotatable mirrors 802 and second rotatable mirror 804 canindependently change the angle of output projection path 219 (orincident light direction 239) with respect to, respectively, the x-axisand the z-axis, to form a two-dimensional FOV. The rotation of array offirst rotatable mirrors 802 and second rotatable mirror 804 can becontrolled based on a movement sequence. Similar to the arrangementsdescribed in FIG. 4, first dimension control signals can be provided ata relatively high frequency close to the natural frequency of array offirst rotatable mirrors 802 to induce harmonic resonance, whereas seconddimension control signals can be provided at a relatively low frequencyto drive second rotatable mirror 804 as quasi-static loads.

FIG. 9 illustrates a flowchart of method of operating a mirror assembly,according to embodiments of the disclosure. FIG. 9 shows a simplifiedflow diagram of method 800 for performing light steering operation usinga mirror assembly, such as mirror assemblies 300, 500, 600,700 and 800of FIG. 3A-FIG. 8. The mirror assembly comprises an array of firstrotatable mirrors (e.g., array of first rotatable mirrors 302, array ofsecond rotatable mirrors 504, etc.) and a second rotatable mirror (e.g.,second rotatable mirror 304, first rotatable mirror 502, secondrotatable mirror 704, etc.). The array of first rotatable mirrors may bepart of a MEMS system and the second adjustable mirror may be part of aMEMS system (e.g., in mirror assemblies 300, 500, 600 and 700) or anon-MEMS system (e.g., in mirror assemblies 800) such as an analogsystem that includes at least one of a galvanometer mirror, a mirrorpolygon or a flash lens. Method 400 may be performed by a controller,such as LiDAR controller 206.

At operation 902, the controller determines a first angle and a secondangle of a light path. In some embodiments, the light path may be one ofa projection path for output light or an input path of input light, thefirst angle may be with respect to a first dimension and the secondangle may be with respect to a second dimension orthogonal to the firstdimension. The first angle may be set according to a scanning pattern(e.g., a sinusoidal scanning trajectory along the fast axis) withinrange 234. The second angle may be set according to the scanning pattern(e.g., sawtooth scanning trajectory or a triangle scanning trajectoryalong the slow axis) within range 238.

At operation 904, the controller controls an array of first actuators torotate an array of first rotatable mirrors of the MEMS to set the firstangle. The controller may also control the array of first actuators toexert a torque to each rotatable mirror of the array of first rotatablemirrors as a quasi-static load.

At operation 906, the controller controls a second actuator of a MEMS ora non-MEMS system to set the second angle. In some embodiments, thecontroller may control the second actuator to exert a torque to thesecond rotatable mirror using a non-MEMS system (e.g., a galvanometermirror or a polygon mirror). In some other embodiments, the controllermay change the mirror within a flash system (e.g., an array of identicalmirrors) to move the light beam within range 238 of scanning pattern232. In some embodiments, the controller may control the second actuatorto exert a torque to the second rotatable mirror using a MEMS, similarto rotating the array of first rotatable mirrors of the MEMS to set thefirst angle.

At operation 908, the controller uses the array of first rotatablemirrors set at the first angle and the second rotatable mirror set atthe second angle to perform at least one of: reflecting the output lightfrom the light source along the projection path towards an object orreflecting the input light propagating along the input path to areceiver. For example, the controller may control a light source toproject a light beam including a light signal towards the mirrorassembly. The light source may include a pulsed laser diode, a source ofFMCW signal, a source of AMCW signal, etc. The controller may also usethe array of first rotatable mirrors and the second rotatable mirror todirect light signal reflected by the distant object to a receiver andnot to direct light signals received at other directions to thereceiver.

In some embodiments, the mentioned method 900 may be implemented on acomputer system utilizing any suitable number of subsystems. Examples ofsuch subsystems are shown in FIG. 10 in computer system 10. In someembodiments, a computer system includes a single computer apparatus,where the subsystems may be the components of the computer apparatus. Inother embodiments, a computer system may include multiple computerapparatuses, each being a subsystem, with internal components. Acomputer system may include desktop and laptop computers, tablets,mobile phones and other mobile devices. In some embodiments, a cloudinfrastructure (e.g., Amazon Web Services), a graphical processing unit(GPU), etc., may be used to implement the disclosed techniques,including the techniques described from FIG. 1-FIG. 9. For example,computer system 10 may be used to implement the functionality of LiDARcontroller 206 and to perform the operations of method 400.

The subsystems shown in FIG. 10 are interconnected via a system bus 75.Additional subsystems such as a printer 74, keyboard 78, storagedevice(s) 79, monitor 76, which is coupled to display adapter 82, andothers are shown. Peripherals and input/output (I/O) devices, whichcouple to I/O controller 71, may be connected to the computer system byany number of means known in the art such as input/output (I/O) port 77(e.g., USB, FireWire®). For example, I/O port 77 or external interface81 (e.g. Ethernet, Wi-Fi, etc.) may be used to connect computer system10 to a wide area network such as the Internet, a mouse input device, ora scanner. The interconnection via system bus 75 allows the centralprocessor 73 to communicate with each subsystem and to control theexecution of a plurality of instructions from system memory 72 or thestorage device(s) 79 (e.g., a fixed disk, such as a hard drive, oroptical disk), as well as the exchange of information betweensubsystems. The system memory 72 and/or the storage device(s) 79 mayembody a computer readable medium. Another subsystem is a datacollection device 85, such as a camera, microphone, accelerometer, andthe like. Any of the data mentioned herein may be output from onecomponent to another component and may be output to the user.

A computer system may include a plurality of the same components orsubsystems, e.g., connected together by external interface 81 or by aninternal interface. In some embodiments, computer systems, subsystem, orapparatuses may communicate over a network. In such instances, onecomputer may be considered a client and another computer a server, whereeach may be part of a same computer system. A client and a server mayeach include multiple systems, subsystems, or components.

Aspects of embodiments may be implemented in the form of control logicusing hardware (e.g. an application specific integrated circuit or fieldprogrammable gate array) and/or using computer software with a generallyprogrammable processor in a modular or integrated manner. As usedherein, a processor includes a single-core processor, multi-coreprocessor on a same integrated chip, or multiple processing units on asingle circuit board or networked. Based on the disclosure and teachingsprovided herein, a person of ordinary skill in the art will know andappreciate other ways and/or methods to implement embodiments of thepresent invention using hardware and a combination of hardware andsoftware.

Any of the software components or functions described in thisapplication may be implemented as software code to be executed by aprocessor using any suitable computer language such as, for example,Java, C, C++, C#, Objective-C, Swift, or scripting language such as Perlor Python using, for example, conventional or object-orientedtechniques. The software code may be stored as a series of instructionsor commands on a computer readable medium for storage and/ortransmission. A suitable non-transitory computer readable medium mayinclude random access memory (RAM), a read only memory (ROM), a magneticmedium such as a hard-drive or a floppy disk, or an optical medium suchas a compact disk (CD) or DVD (digital versatile disk), flash memory,and the like. The computer readable medium may be any combination ofsuch storage or transmission devices.

Such programs may also be encoded and transmitted using carrier signalsadapted for transmission via wired, optical, and/or wireless networksconforming to a variety of protocols, including the Internet. As such, acomputer readable medium may be created using a data signal encoded withsuch programs. Computer readable media encoded with the program code maybe packaged with a compatible device or provided separately from otherdevices (e.g., via Internet download). Any such computer readable mediummay reside on or within a single computer product (e.g. a hard drive, aCD, or an entire computer system), and may be present on or withindifferent computer products within a system or network. A computersystem may include a monitor, printer, or other suitable display forproviding any of the results mentioned herein to a user.

Any of the methods described herein may be totally or partiallyperformed with a computer system including one or more processors, whichmay be configured to perform the steps. Thus, embodiments may bedirected to computer systems configured to perform the steps of any ofthe methods described herein, potentially with different componentsperforming a respective step or a respective group of steps. Althoughpresented as numbered steps, steps of methods herein may be performed ata same time or in a different order. Additionally, portions of thesesteps may be used with portions of other steps from other methods. Also,all or portions of a step may be optional. Additionally, any of thesteps of any of the methods may be performed with modules, units,circuits, or other means for performing these steps.

Other variations are within the spirit of the present disclosure. Thus,while the disclosed techniques are susceptible to various modificationsand alternative constructions, certain illustrated embodiments thereofare shown in the drawings and have been described above in detail. Itshould be understood, however, that there is no intention to limit thedisclosure to the specific form or forms disclosed, but on the contrary,the intention is to cover all modifications, alternative constructionsand equivalents falling within the spirit and scope of the disclosure,as defined in the appended claims. For instance, any of the embodiments,alternative embodiments, etc., and the concepts thereof may be appliedto any other embodiments described and/or within the spirit and scope ofthe disclosure.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the disclosed embodiments (especially in thecontext of the following claims) are to be construed to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context. The terms “comprising,” “having,” “including,”and “containing” are to be construed as open-ended terms (i.e., meaning“including, but not limited to,”) unless otherwise noted. The term“connected” is to be construed as partly or wholly contained within,attached to, or joined together, even if there is something intervening.The phrase “based on” should be understood to be open-ended, and notlimiting in any way, and is intended to be interpreted or otherwise readas “based at least in part on,” where appropriate. Recitation of rangesof values herein are merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range,unless otherwise indicated herein, and each separate value isincorporated into the specification as if it were individually recitedherein. All methods described herein may be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate embodiments of the disclosure and does not pose a limitationon the scope of the disclosure unless otherwise claimed. No language inthe specification should be construed as indicating any non-claimedelement as essential to the practice of the disclosure.

What is claimed is:
 1. An apparatus for adjusting a light beam,comprising: a microelectromechanical system (MEMS), comprising: an arrayof rotatable mirrors configured to receive and reflect the light beam;and an array of first actuators configured to rotate each rotatablemirror of the array of rotatable mirrors through a first range ofscanning angles in a first dimension by applying a first actuation forceto each rotatable mirror in the array of rotatable mirrors; and anon-MEMS system, comprising: a single rotatable mirror configured toreceive and reflect the light beam; and a second actuator configured torotate the single rotatable mirror through a second range of scanningangles in a second dimension by applying a second actuation force to thesecond actuator; wherein the first actuation force is no larger than thesecond actuation force, and wherein the first range of scanning anglesis greater than or equal to the second range of scanning angles.
 2. Theapparatus of claim 1, wherein the array of rotatable mirrors and thesingle rotatable mirror are configured to set a first angle of lightpath of the light beam with respect to a first dimension and to set asecond angle of the light path of the light beam with respect to asecond dimension orthogonal to the first dimension respectively.
 3. Theapparatus of claim 2, further comprising a controller configured to:control the array of first actuators and the second actuator to output afirst light including a first light signal at a first time point alongthe light path towards an object; control the array of first actuatorsand the second actuator to select a second light including a secondlight signal propagating along the light path from the object; receive,via a receiver, the second light at a second time point; and determine alocation of the object with respect to the apparatus based on adifference between the first time point and the second time point, thefirst angle, and the second angle.
 4. The apparatus of claim 3, whereinthe controller is further configured to: adjust a first rotation angleof each rotatable mirror of the array of rotatable mirrors at a firstfrequency, the first frequency being a natural frequency of the array ofrotatable mirrors; and adjust a second rotation angle of the singlerotatable mirror at a second frequency lower than the first frequency.5. The apparatus of claim 1, wherein the non-MEMS system is an analogsystem including at least one of a galvanometer mirror, a mirrorpolygon, or a flash lens.
 6. The apparatus of claim 5, furthercomprising a third mirror facing the array of rotatable mirrors and thesingle rotatable mirror and is configured to reflect the light beamreflected from the array of rotatable mirrors towards the singlerotatable mirror.
 7. The apparatus of claim 6, further comprising asemiconductor substrate, wherein the third mirror is separated fromsurface of the semiconductor substrate by a first distance; wherein thearray of the rotatable mirrors and the single rotatable mirror areseparated by a second distance; and wherein the first distance and thesecond distance are set based on an angle of incidence of the light beamfrom a light source with respect to the first rotatable mirror.
 8. Theapparatus of claim 7, further comprising a collimator lens, wherein thecollimator lens is positioned between the light source and the array ofrotatable mirrors, and wherein the collimator lens has a pre-determinedaperture length.
 9. The apparatus of claim 8, wherein the light sourceis a laser diode.
 10. The apparatus of claim 1, wherein each actuator ofthe array of first actuators comprises at least one of a comb drive, apiezoelectric device, or an electromagnetic device.
 11. A LightDetection and Ranging (LiDAR) system comprising: a light sourceconfigured to emit a light beam; a receiver; a microelectromechanicalsystem (MEMS) comprising: an array of rotatable mirrors to receive andreflect the light beam; and an array of first actuators configured torotate each rotatable mirror of the array of rotatable mirrors through afirst range of scanning angles associated with a first dimension byapplying a first actuation force to each rotatable mirror in the arrayof rotatable mirrors; and a non-MEMS system comprising: a singlerotatable mirror to receive and reflect the light beam; and a secondactuator configured to rotate the single rotatable mirror through asecond range of scanning angles associated with a second dimension byapplying a second actuation force to the second actuator, wherein thefirst actuation force is no larger than the second actuation force, andwherein the first range of scanning angles is greater than or equal tothe second range of scanning angles.
 12. The system of claim 11, whereinthe array of rotatable mirrors and the single rotatable mirror areconfigured to set a first angle of light path of the light beam withrespect to a first dimension and to set a second angle of the light pathof the light beam with respect to a second dimension orthogonal to thefirst dimension respectively.
 13. The system of claim 12, furthercomprising a controller configured to: control the array of firstactuators and the second actuator to output a first light including afirst light signal at a first time point along the light path towards anobject; control the array of first actuators and the second actuator toselect a second light including a second light signal propagating alongthe light path from the object; receive, via a receiver, the secondlight at a second time point; and determine a location of the objectbased on a difference between the first time point and the second timepoint, the first angle, and the second angle.
 14. The system of claim11, wherein the non-MEMS system is an analog system including at leastone of a galvanometer mirror, a polygon mirror or a flash lens.
 15. Thesystem of claim 14, further comprising a third mirror facing the arrayof rotatable mirrors and the single rotatable mirror and is configuredto reflect the light beam reflected from the array of rotatable mirrorstowards the single rotatable mirror.
 16. The system of claim 15, furthercomprising a semiconductor substrate, wherein the third mirror isseparated from a surface of the semiconductor substrate by a firstdistance; wherein the array of the first rotatable mirrors and thesingle rotatable mirror are separated by a second distance; and whereinthe first distance and the second distance are set based on an angle ofincidence of the light beam from a light source with respect to thefirst rotatable mirror.
 17. The system of claim 16, further comprising acollimator lens, wherein the collimator lens is positioned between thelight source and the first rotatable mirror, and wherein the collimatorlens has a pre-determined aperture length.
 18. The system of claim 11,wherein the light source is a laser diode.
 19. The system of claim 11,wherein each actuator of the array of first actuators comprises at leastone of: a comb drive, a piezoelectric device, or an electromagneticdevice.
 20. A method of operating an optical steering system,comprising: applying, using an array of first actuators, a firstactuation force to each rotatable mirror in an array ofmicroelectromechanical system (MEMS) mirrors to rotate the array of MEMSmirrors through a first range of scanning angles in a first dimension;applying, using a second actuator, a second actuation force to a singlerotatable mirror to rotate the single rotatable mirror through a secondrange of scanning angles in a second dimension, the second directionbeing orthogonal to the first direction; and steering, by the array ofMEMS mirrors and the single rotatable mirror, a light beam through thefirst range of scanning angles in the first dimension and second rangeof scanning angles the second dimension, respectively, wherein the firstactuation force is no larger than the second actuation force, andwherein the first range of scanning angles is greater than or equal tothe second range of scanning angles.